Liquid crystal display devices are widely used as the screens of cell phones, personal computers, TV monitors, and the like. Specifically for example, their demand has been increasing in TVs and the like. The liquid crystal display device is generally composed of a liquid crystal display element and a lighting unit having a light source such as a cold cathode fluorescent lamp which irradiates the element. The light source irradiates the liquid crystal display element to form an image. The manner of emitting light to the liquid crystal display element includes: a frontlight type which emits light from the front of the liquid crystal display element; and a backlight type which emits light from the rear of the liquid crystal display element. The backlight type is further grouped into a direct type which irradiates the element from the rear with light from the light source, and an edge type which irradiates the element from the side.
In order to emit light to a liquid crystal display element uniformly over the whole area to attain a high level in display quality, the backlight type, for example, needs a light-diffusing plate to diffuse light from a light source uniformly.
Conventional light-diffusing plate is made of an acrylic resin because of the high light transmittivity to give high luminance. Acrylic resin, however, likely absorbs moisture depending on the use conditions, resulting in deflection and warp brought about in the light-diffusing plate to deteriorate the dimensional stability. In recent years, the increasing demand of a large scaled liquid crystal display device for use in a big TV and the like requires the excellent dimensional stability. Furthermore, there are requested also the durability against ultraviolet light generated from a light source and the flame retardancy.
There is also disclosed a light-diffusing plate prepared by mixing a polycarbonate resin with a light-diffusing agent, (for example, refer to Patent Document 1). The polycarbonate resin is excellent in property such as dimensional stability and heat resistance. However, the polycarbonate resin has a relatively high refractive index and is inferior in light transmittivity. Accordingly, the polycarbonate resin is used for the light-diffusing plate in a liquid crystal display device, to decrease the luminance of the device. A means is demanded to improve the optical characteristics of the light-diffusing plate.
Furthermore, to improve the light diffusibility and the impact resistance, there are disclosed a light-diffusing plate prepared by mixing an acrylic resin with a light-diffusing agent and a rubber-like polymer, (for example, refer to Patent Document 2), a light-diffusing plate prepared by mixing a transparent resin with a specific liquid crystal polymer, (for example, refer to Patent Document 3), and a light-diffusing sheet using an epoxy resin layer with a mixed light-diffusing agent, a gas-barrier layer, and an urethane-acrylate resin layer, (for example, refer to Patent Document 4). All of these light-diffusing plates and light-diffusing sheet, however, need a means for maintaining or improving the luminance with the assured light diffusibility and further suppressing the dimensional changes caused by moisture absorption, while preventing the device from deterioration caused by ultraviolet light generated- from the lighting unit.
In order to improve the durability against ultraviolet light, there is disclosed a liquid crystal display device having a layer for cutting the ultraviolet light between the light source and the liquid crystal display element, (for example, refer to Patent Document 5). The disclosed liquid crystal display device, however, need a means for further improving the display quality of the liquid crystal display device by suppressing the dimensional changes caused by moisture absorption while improving the luminance of the liquid crystal display device. There is also disclosed a laminated product comprising a polycarbonate resin layer laminated with acrylic resin layer, (for example, refer to Patent Document 6). That kind of laminated product, however, is generally used for lighting material, sound-proof wall, and the like. The laminated product, which is improved in light transmittivity and light diffusibility to give a light-diffusing plate suitable for use in a liquid crystal display device, further needs a means for the light-diffusing plate to improve the liquid crystal display device in display quality.
On the other hand, as a resin composition suitable for use in a light-diffusing plate, there is disclosed a light-diffusing resin composition composed of an aromatic polycarbonate-based resin containing a block of polyorganosiloxane, and a cross linked acrylic resin bead, (for example, refer to Patent Document 7). The light-diffusing plate using the resin composition, however, needs a means for further improving the light transmittance with the assured sufficient light diffusibility, thereby to give excellent optical characteristics, and to allow suitable application also for the liquid crystal display devices in household electric appliances.
[Patent Document 1] JP5-257002, A (1993) (the term “A” referred to herein signifies the “Patent application Laid-open”).
[Patent Document 2] JP11-105207, A (1999)
[Patent Document 3] JP11-231113, A (1999)
[Patent Document 4] JP2002-351353, A
[Patent Document 5] JP10-333140, A (1998)
[Patent Document 6] JP6-71832, A (1994)
[Patent Document 7] JP10-46022, A (1998)